AndyA - 12:42 pm on May 7, 2010 (gmt 0)
You can turn off interest based ads. If this is repetitious, sorry!
This does not turn off interest-based ads on your site. It only prevents Google from using your site's visitors information while they're on your site.
They still see interest based ads, but if your site is about gardening, their time spent on your site won't be used to show gardening ads to them in the future.
The reason Google has this option is for those who have privacy policies that specifically state visitors actions aren't tracked on a site.
The comment about searching for a book, buying it, and then seeing ads for that book for days later is a good one. Most people aren't going to buy multiple copies, and if they were they'd have done it with the original purchase, or they'd go back to that same site to buy another one.
What interested me yesterday is of no interest today. I've moved on. How could Google possibly know differently?